Oxidos mistos e microporosos preparados pelo metodo sol-gel como catalisadores para a oxidação de hidrocarbonetos em fase liquida

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

Mixed Cr2O3-, CuO-, and Mo2O5 oxides in SiO2 were sintetized by the sol-gel process, using acid catalysis, slow solvent drying, and soft thermal treatment, with slow temperature increase, which favours a narrow micropore distribution. The prepared mixed oxides were characterized by elemental analysis, XRD, nitrogen adsorption - desorption, IR and UV-vis, EPR, TPR and SEM-EDS. The characterization results show that Cr was partially incorporated in the silica matrix, in an octahedral coordination. Some species, possibly oxides, are highly dispersed on the material surfaces and were removed by soxhlet extraction, resulting in a stable catalyst with good activity in cyclohexane oxidation with terc-butyl hydroperoxide. The conversions were higher than 4%, TN = 212, and the product selectivity [ona + ol + CHHP] was 84%. However, part of this activity is attributed to homogeneous catalysis by species leached from the solids by the oxidant. There were no evidences for Cu incorporation in the silica matrix, but copper species were observed highly dispersed in the surface. The catalysts are less active in cyclohexane oxidation (NT = 134, product selectivity = 64%) an intensive material leaching was observed, although these leached species are not active in the homogeneous phase oxidation. Stable Si-O-Mo materials were obtained, but the presence of more than one species of Mo was detected, and partial oxidation of Mo(V) occurred during the sol-gel process. The Mo(iPr)-SiO2 catalyst was shown to be truly heterogeneous, stable and very active in cyclooctene epoxidation (conversion = 82%, selectivity = 95%, NT = 1590), and could be recycled at least three times without loss of activity.

ASSUNTO(S)

metais de transição oxidação catalise heterogenea

ACESSO AO ARTIGO

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